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6281424988
The conversion of window icon image data involves unsigned char color
values being promoted to int and then shifted to the left by 24. For
32-bit ints this is just far enough to trigger undefined behavior.
It worked by accident because of how current compilers translate this
piece of code.
This was caught by @slimsag while working on [Zig bindings for GLFW][1],
and diagnosed together with @Andoryuuta, as described [in an
article][2]. Zig has UBSan enabled by default, which caught this
undefined behavior.
[1]: https://github.com/hexops/mach-glfw
[2]: https://devlog.hexops.com/2021/perfecting-glfw-for-zig-and-finding-undefined-behavior#finding-lurking-undefined-behavior-in-6-year-old-glfw-code
Thanks to Maato, martinhath, dcousens, drfuchs and Validark for helping
to refine the solution.
This commit message was rewritten by @elmindreda to hopefully reflect
the conclusions of the pull request thread.
Related to hexops/mach#20
Closes #1986
(cherry picked from commit 9cd4d2fa20)